Phosphorus is a poison to noble metal catalysts in the chemical industry. By the same token, studies undertaken by the American Automobile Manufacturers Association (AAMA) have also shown that phosphorus will poison the emission control catalysts in today's automobiles. For that reason, the AAMA and more recently the International Lubricant Standardization and Approval Committed (ILSAC), have placed limits on the amount of phosphorus to be allowed in engine oils, with the long term goal of lowering the phosphorus content enough to render it harmless to automobile catalytic converters. The latest standard, GF-3, limits the phosphorus to no more than 0.1% by weight in motor oils.
One problem with eliminating phosphorus from motor oil formulations is that it provides the polar attractive forces that attach the lubricant molecules to the metal surface, forming an energy-absorbing barrier against friction and wear. Phosphorus-containing additives work in a unique energy band, providing low friction and high wear protection to metals at light to medium loads, such as those found in piston rings and cam followers in an engine. Phosphorus also has the attributes of not forming ash, low toxicity, and being non-metalic. The limit on phosphorus has caused a controversy between the AAMA/ILSAC designers and the formulators of motor oils (Lubes and Greases November, 1998).
Traditional lubricity additives contain lead, sulfur, phosphorous, zinc, nitrogen or boron. Lead is now banned. The other additives have been shown to be ash forming or catalyst-poisoning. These additives are thermally activated and form sacrificial chemical bonds to metal surfaces. The bonded additive will then “shear” from the metal surface before the metal itself, resulting in protection of the metal surface from wear. Many additives also contribute to particulate formation, or sludging, during oxidation. Moreover, motor oil lubricity additives can form SOx, NOx and POx emissions, or emissions which can poison the catalysts used in catalytic converters, causing an increase in particulate and hydrocarbon emissions.
Therefore there is a need in the art for lubricity additives that impart needed lubricity properties but provide minimal ash or preferably ash-less properties for the purposes of reducing ultimate pollution and emission characteristics. The invention describes the achievement of that goal.